This invention may be described as an improved reciprocating air compressor which is attached to an electric drive motor and provides for a high pressure air supply for locomotives and is designed to include a third crankshaft bearing that is contained in an extended bearing housing, which is detachable from the crankcase to decrease crankshaft deflection.
It is known to use multi-cylinder air compressors on freight and passenger locomotives. The compressors supply compressed air to the operating and control equipment of a railway air brake system. Generally in a reciprocating compressor one or more pistons are connected to a crankshaft by use of connecting rods. As the crankshaft turns, the connecting rods reciprocate the pistons in cylinders causing the compression of air. Air compressors are designed so that the crankshaft is supported by a pair of main bearings located on opposite ends of the crankshaft. The crankshaft extends outwardly from the compressor crankcase and is connected to an integrated inline electric motor. With only two bearings supporting the crankshaft the extended length and the weight of the overhung rotor causes considerable deflection of the extended crankshaft thereby causing an non-uniform motor air gap. The non-uniform air gap generates an unbalanced magnetic pull during the start up of the motor, which in turn increases the crankshaft deflection. This deflection can be large enough to cause rubbing between the rotor and the stator of the compressor drive motor. These deflections are exacerbated due to the length of the shaft connecting the compressor to the electric motor. To compensate for the movement of the rotor caused by deflections in the crankshaft, the air gap between the stator core and the rotor on the prior art devices is increased to prevent stator to rotor contact. This increased gap however, decreases the efficiency of the electric motor and does not always prevent rotor to stator rubbing.
This invention may be described as an air compressor for locomotives that allows for the direct attachment of an electric motor and provides for an extended crankcase housing that includes an outboard crankshaft bearing to eliminate deflections in the crankshaft and rotor. The elimination of deflections in the crankshaft allows for a more uniform and reduced air gap between the stator and the rotor of the electric motor, increasing the motor""s efficiency and eliminating the opportunity of rotor to stator contact. The electric motor is adapted to allow the extended crankcase housing to fit within the rotor of the motor, placing the outboard crankshaft support bearing closer to the rotor than conventional designs and significantly reducing the overall overhang of the crankshaft. The outboard crankshaft support bearing is enclosed in an extended bearing housing that is removable from the crankcase to facilitate maintenance. A shorter crankshaft overhang has less deflection, reducing unwanted rotor movement. The locomotive air compressor includes a crankcase with three reciprocating pistons connected to a common crankshaft. The crankshaft is supported by two main bearings on opposite sides of the crankcase. The air compressor also includes the removable extended bearing housing that includes the outboard crankshaft support bearing to prevent crankshaft deflection. The extended crankshaft housing is adapted to accept an integrated electric motor. The electric motor rotor is adapted to be connected to the crankshaft. The extended housing of the outboard bearing provides for a more rigid support structure for the motor rotor, which reduces the length of the overhung shaft to reduce crankshaft deflection. Also the side load created by the unbalanced magnetic pull by the electric motor is transferred to the extended bearing housing which further prevents unwanted movement. Since the outboard bearing is fluidly connected to the compressor crankcase, lubricating oil can adequately be fed to and returned from the bearing, eliminating the need for a separate bearing oiling system.